The latest versions of SHELD Experience SW includes a Develop Option "Force allow apps on external".
When enabled, this will force newly installed apps to be stored on adopted storage connected to your SHIELD TV (USB or SD).
This feature should be used with caution. In many cases, apps installed on adopted storage cannot be updated from the Google Play Store. To update your app, you will need to
1. Move your app from adopted storage back to internal
2. Uninstall the app and re-install from the Google Play Store